<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <button id="btn">点击发送ajax</button>
  <script>
    const btn = document.getElementById('btn')
    function sendAjax(url) {
      return new Promise((resolve, reject) => {
        // 1.创建对象
        const xhr = new XMLHttpRequest()
        // 2.初始化
        xhr.open('GET', url)
        // 3.发送
        xhr.send()
        // 4.绑定事件处理响应结果
        xhr.onreadystatechange = function() {
          if (xhr.readyState === 4) {
            // 判断状态码
            if (xhr.status >= 200 && xhr.status < 300) {
              // 控制台输出响应体
              resolve(xhr.response)
            } else {
              // 控制台输出响应状态码
              reject(xhr.status)
            }
          }
        }
      })
    }
    btn.addEventListener('click', async function() {
      let duanzi = await sendAjax('https://api.apiopen.top/getJoke')
      console.log(duanzi);
    })
  </script>
</body>
</html>